A construction machine or the like includes a cooling fan which rotates to supply air to a radiator to cool the radiator. As a driving source for the cooling fan, for example, a hydraulic motor is used. The hydraulic motor is configured to receive pressurized oil supplied from a hydraulic drive device and rotate the cooling fan. As one example of such a hydraulic drive device, a hydraulic drive cooling fan device disclosed in Patent Literature 1 is known.
The hydraulic drive cooling fan device disclosed in Patent Literature 1 includes a pilot pump and a steering pump. The pilot pump is configured to discharge pressurized oil for a pilot pressure to a pilot circuit. The steering pump is a variable displacement pump which changes the flow rate of the discharged oil, depending on the water temperature of the radiator. The steering pump is configured to supply the pressurized oil to a steering via a steering circuit. The steering circuit is divided at a point and merges into the pilot circuit. The steering circuit and the pilot circuit constitute a merge circuit. The merge circuit is connected to a hydraulic motor, which receives a hydraulic pressure from the merge circuit, thereby rotating the cooling fan.
In the hydraulic drive cooling fan device configured as described above, when the water temperature of the radiator is low, the oil is discharged from the steering pump at a low flow rate and the cooling fan is rotated at a low speed so that the water temperature of the radiator is increased. On the other hand, when the water temperature of the radiator is high, the oil is discharged from the steering pump at a high flow rate and the cooling fan is rotated at a high speed so that the water temperature of the radiator is decreased.